A. Field of the Invention PA1 B. Alkylene Oxide-Styrene Monomer Production Processes PA1 C. Prior 2-Phenylethanol Production Processes PA1 "In the .beta.-phenylethyl alcohol obtained by these methods, however, various aromatic hydrocarbons or alcohols possessing aromatic radicals other than .beta.-phenylethyl alcohol are present as impurities such as di-phenyl, di-benzyl, di-phenylmethane, 3-phenyl propanol, .alpha.-phenylethyl alcohol and -(2-hydroxy-ethoxy) ethylbenzene." PA1 ". . . by discovering that although .beta.-phenyl alcohol easily forms an addition product with qualified metal halides, alcohols possessing an aromatic radical other than .beta.-phenylethyl alcohol and aromatic hydrocarbon impurities either do not form any addition products at all or form additions that do not exceed a very small quantity." PA1 "Our current understanding of the factors which determine selectivity is very limited. In general one must simply try this purification technique on the alcohol mixture in question to learn what the outcome will be. The empirical nature of this method should diminish as its use increases. In any case, we have observed certain effects which are worth pointing out. While discussing these factors individually, it is important to realize that although trends can be discerned for isolated factors, the actual effect on the selectivity is a complex function of all of the factors. Thus most of the following statements should be prefaced by the phrase `other things being equal.`" PA1 "More recently we have sought to establish an optimum set of reaction conditions to be tried first on any new mixture. The factors to be optimized are, of course, selectivity and the recovery--the product of these two determines the yield of the desired component isolated from the mixture. Unfortunately, this has not been easy, since each mixture seems to respond differently to the controllable variables." (emphasis added) (at page 1253)
The present invention relates generally to the field of alkylene oxide-styrene monomer production processes, and more particularly to methods for recovering and refining by-products resulting from those processes. The present invention also relates to methods for producing 2-phenylethanol, and thus also pertains to methods for purifying 2-phenylethanol from mixtures containing other materials, such as methylbenzyl alcohol, benzyl alcohol, acetophenone, phenyl propanols, etc.
In one prior process for producing alkylene oxides, e.g., propylene oxide and styrene monomer, ethylbenzene is oxidized with air in a series of oxidizers to give a solution of ethylbenzene hydroperoxide in ethylbenzene. During this oxidation, some by-products are formed, notably methylbenzyl alcohol and acetophenone, and in minor amounts 2-phenylethanol and its precursors, e.g., 2-phenylethyl hydroperoxide. This solution of ethylbenzene hydroperoxide is then concentrated in successive steps of distillation, and unreacted ethylbenzene is recycled for oxidation.
Ethylbenzene hydroperoxide is then typically used to epoxidize the olefinically unsaturated compound, e.g., propylene, to propylene oxide, in the presence of a suitable catalyst. In this process, the hydroperoxide itself is converted to methylbenzyl alcohol. By-products of this reaction include more acetophenone, phenol, benzaldehyde, 2-phenylethanol, unreacted reactants, and high boiling materials.
Excess propylene in the aforementioned propylene oxide epoxidation product is normally removed by distillation. Propylene oxide may then be removed by distillation as a crude product, leaving a stream comprising excess ethylbenzene, the aforementioned by-products, and residues. The stream is then distilled to recover ethylbenzene overheads, leaving an aromatic rich distilland comprising methylbenzyl alcohol, acetophenone, and a variety of other by-products, including 2-phenylethanol. The composition of such distilland may vary widely and comprises a variety of alcohols, ketones and other by-products. (See Table I.)
In a typical propylene oxide-styrene monomer production process, the aforementioned methylbenzyl alcohol/acetophenone distilland (bottoms stream) is purified through distillation, and then is fed to styrene production reactors where it is contacted in the liquid phase with a suitable dehydration catalyst to convert methylbenzyl alcohol to styrene. After removing styrene from the dehydration reaction product by distillation, there is produced an acetophenone-rich bottoms product which is then hydrogenated using a suitable catalyst to convert acetophenone to methylbenzyl alcohol, which may then be recycled for styrene production.
Further information concerning the production of propylene oxide and styrene monomer are described in U.S. Pat. Nos. 3,403,193 (Russell) entitled "Process for the Co-Production of a Styrene and an Di-Olefin;" 3,4052,055 (Golden, et al) entitled "Process for the Recovery Epoxides Where an Alkylaromatic Compound is Removed in Two Distillation Zones," and 3,928,393 (Herzog) entitled "Process for the Preparation of Oxirane Compounds." In U.S. Pat. No. 3,403,193, for example, a styrene-diolefin production process similar to that described above is disclosed; from the following it will be seen that the present invention relates to the recovery of 2-phenylethanol from streams such as streams 9, 12, 15, 19, and more preferably 17, as disclosed in this patent.
In U.S. Pat. Nos. 3,526,674 (Becker, et al) entitled "Process for the Dehydration of Aralkanols," 3,442,963 (Korchak) entitled "Dehydration of Methyl Benzyl Alcohol to Styrene," 3,925,496 (Shalit, et al) entitled "Production of Styrene," 2,866,832 (Fenoglio, et al) entitled "Process for the Dehydration of Dimethylphenyl-carbinol" and 3,459,810 (Choo, et al) entitled "Process for the Preparation of Ethyl Benzene Hydroperoxide," other related production processes are disclosed, including processes which may be useful in the production of styrene through similar dehydration processes.
Heretofore, 2-phenylethanol (-phenylethanol, phenylethyl alcohol, or phenylethyl alcohol, 2-phenylethyl alcohol benzylcarbinol) has generally been produced using any one of three commercially viable methods. Thus 2-phenylethanol has been produced commercially by using a Friedel-Crafts reaction of benzene and ethylene oxide (in the presence of aluminum trichloride) to produce primary yields in excess of about 90% 2-phenylethanol. The direct reduction of styrene oxide has also been utilized to produce primary yields of 2-phenylethanol in excess of about 90%. Such reductions are typically conducted by contacing catalysts, such as nickel, with hydrogen and styrene oxide to produce the aforementioned 2-phenylethanol product. A third commercially viable method for producing 2-phenylethanol involved the Grignard reaction of phenyl magnesium bromide with ethylene chlorohydrin. This method also results in primary yields of 2-phenylethanol which exceed about 90%.
Since the yields of the above-described methods are quite high, and the by-products of such processes are limited in number and amount, purification of such 2-phenylethyl alcohol products is relatively straightforward. When the aforementioned Grignard method is used to produce 2-phenylethyl alcohol, the major impurity in the reaction product which cannot be removed by simple distillation is diphenyl (biphenyl). U.S. Pat. No. 2,114,286, (which references British Pat. No. 398,561 of 1933) indicates that it is known to distill a crude Grignard reaction mixture to obtain a fraction consisting substantially of 2-phenylethyl alcohol and diphenyl, to then dissolve this fraction in benzene, treat it at room temperature with calcium chloride to form an insoluble 2-phenylethyl alcohol-calcium chloride double compound, separate the latter and wash the same with fresh benzene, then decompose the double compound with water, shaking the recovered alcohol with toluene, and finally distilling to recover the purified alcohol. U.S. Pat. No. 2,114,286 also discloses that some of the disadvantages associated with this procedure can be overcome by heating impure 2-phenylethyl alcohol containing diphenyl (or other impurities which do not react with calcium chloride) with anhydrous calcium chloride and an organic solvent to a temperature above 80.degree. C., and then allowing the mixture to cool. A 2-phenylethyl alcohol-calcium chloride compound will then be obtained in the form of relatively large, well defined crystals which may be readily separated from the liquor by filtration and washed free of adherent impurities.
In U.S. Pat. No. 2,068,145 entitled "Purification of Alcohols," phenylethyl alcohol prepared by a Friedel-Crafts reaction of benzene with ethylene oxide in the presence of anhydrous aluminum chloride is disclosed as producing a product containing impurities, such as dibenzyl and phenylethyl chloride. While recognizing that the addition of calcium chloride has been suggested for purifying phenylethyl alcohol, such purification is described in U.S. Pat. No. 2,068,145 as being "not sufficiently complete." Instead, this patent discloses that phenylethyl alcohol should be treated with an acid which forms a sufficiently stable ester of sufficiently high boiling point so that the impurities may be distilled off. See also U.S. Pat. No. 2,052,881 (Klipstein) entitled "Purification of Alcohols."
In U.S. Pat. No. 3,579,593, the preparation of 2-phenylethyl alcohol is disclosed through the direct reduction of styrene oxide in the presence of two catalysts: Raney nickel and palladium. In U.S. Pat. No. 3,579,593 the use of these catalysts is disclosed as producing yields, based upon the amount of styrene oxide starting material, in excess of 95%, instead of 87-88% yields which may be realized by this process when other catalysts and catalyst mixtures are used. Under these circumstances, fractional distillation of the desired alcohol is disclosed as producing the desired 2-phenylethanol end product.
Other methods for purifying phenylethyl alcohol have also been suggested, and are often described as providing advantages over the method of purification involving the use of anhydrous calcium chloride which is said to be unsatisfactory in readily providing a pure product. See, for example, U.S. Pat. No. 1,752,365 which suggests the use of phthalic anhydride in such a purification.
In Japanese Patent Publication 1979-3026, published Jan. 11, 1979, entitled "A Method for Refining .beta.-phenyl Ethyl Alcohol" (Tani, et al), a method is disclosed for refining 2-phenylethyl alcohol in which an addition product of 2-phenylethyl alcohol and a chloride, bromide or iodide of calcium, magnesium, manganese, or cobalt is formed. After this addition product is separated, 2-phenylethyl alcohol is recovered by dry distillation of said addition product under reduced pressure. After noting that the various methods for preparation of 2-phenylethyl alcohol include the three above-mentioned methods, Japanese patent states:
Accordingly, this Japanese reference teaches such addition products should be formed using such a halide and a solvent which is inactive with respect to the appropriate metal halide and 2-phenylethyl alcohol. For the purpose, an aromatic hydrocarbon such as benzene or toluene, or other solvent such as a saturated hydrocarbon (hexane, pentane, or cyclohexane) solvent may be used which is subsequently separated from the addition product and recycled. In forming this addition product, this Japanese patent discloses that molar ratios of between 0.1:1 to 10:1 of metal halide compound to 2-phenylethyl alcohol may be used. After dry distillation, a 2-phenylethyl alcohol product having a purity in excess of 99.5%, and after simple rectification, with a purity of 99.9%, can be obtained. In support of its disclosure, Japanese Patent Publication 1979-3026 provides seven examples, each of which discloses the purification of crude 2-phenylethyl alcohol products which contain 2-phenylethyl alcohol weight percentages which are typical of those produced by the aforementioned conventional preparation procedures, i.e., crude products containing in excess of about 90% 2-phenylethanol.
In addition to the patents and publications referred to above, please refer to E. German Patentschrifts 112,116 (1975); 112,115 (1975); 112,114 (1975) and 112,643 (1975), as well as to U.S.S.R. Author's Certificate 123,955 entitled "Method for Separating Phenylethyl Alcohol" (Schumeyko, et al) (1959), which describe other methods for purifying 2-phenylethanol materials.
As seen from the above, most prior 2-phenylethanol production techniques rely on high primary yield processes which are followed by any one of the aforementioned purification methods. In these processes, the organic feed solutions from which 2-phenylethanol is separated almost invariably contain more than 90% 2-phenylethanol and less than about 10% by-products.
The principle behind the separation of organic mixtures by formation of metal complexes is discussed in an article entitled "Rapid Separation of Organic Mixtures by Formation of Metal Complexes," by K. Barry Sharpless, et al, J. Org. Chem. 40, 1252--1257 (1975). In this article, Dr. Sharpless notes that mixtures of organic alcohols have been purified for many years by the formation of complexes with calcium chloride and other anhydrous metal halides, however, for "unknown reasons" various metal complexing agents were generally less effective in separating compounds containing functional groups other than alcohols. Dr. Sharpless states:
Thus while the art discloses that certain of the reaction mixtures containing more than about 90% 2-phenylethyl alcohol can be successfully complexed with metal halides, Sharpless teaches that such results do not predict whether 2-phenylethanol can be separated by this method from solutions having markedly different compositions.